The invention relates to an electron gun for heating, melting and vaporizing purposes, having an electron emitting cathode, at least one beam-forming electrode associated with the cathode, an accelerating anode, an electromagnetic lens, and a beam guiding tube extending in the direction of the beam path and surrounded by one electromagnetic deflection system for the x-axis deflection and one for the y-axis deflection, an envelope tube being disposed outside of the deflection system and being connected at its extremity by an end plate to the extremity of the beam guiding tube, the pole shoes of the x-axis deflection system being carried through the said end plate.
German Pat. No. 1,248,175 describes an electron gun of the kind described above, but one which has only one deflection system, in which the end plate, which is not further specified in said patent, is aligned perpendicularly to the longitudinal axis of the gun between the envelope tube or sleeve and the beam guiding tube. This known apparatus did result in a considerable improvement of the gun systems existing at the time; it is nevertheless in need of improvement. For example, the magnetic fields which inevitably occur between the pole pieces of the deflection system result in a perceptible deflection of the electron beam, so that, under unfavorable circumstances, i.e., in the event of a great beam deflection and less than optimum focusing, an incipient fusing has been observed in the discharge orifice, i.e., in the beam guiding tube and in the end plate. Attempts to diminish the magnetic fields at this point by means of an iron ring have not produced the desired success. In the known apparatus, furthermore, the end plate is undesirably heated by the radiant heat emitted by the heated material and also by reflected electrons. When the known electron gun is used for vaporizing purposes and the vaporizing crucible is located in the immediate vicinity of the end of the gun, vapor coating of the end plate has furthermore been observed. This is to be attributed to the fact that the stream of vapor assumes a conical or lobar shape on emerging from the vaporizing crucible, i.e., it diverges upwardly, and thus impinges upon the end plate of the gun system. Upon reaching a certain thickness of build-up at the gun orifice, the material peels off, thereby creating the considerable danger that the material might fall into the vaporizing crucible and contaminate the vaporization material contained therein. This disadvantage is particularly important because different materials have to be vaporized, depending on the application, and they must not be mixed with one another.